1. Field of the Invention
This invention relates to improvements in wheel rims for large wheels of off-highway vehicles and to an improved brake disc for the disc braking apparatus associated with the large wheels.
2. Description of the Prior Art
Extremely large off-highway vehicles are becoming widely used in many industries, such as mining industry, large construction industry, and the like. The excessive size and weight of these vehicles has created many problems in the construction and operation thereof for both efficiency and safety purposes. Of course, the wheels of these vehicles are exceptionally large, usually requiring tires in excess of ten feet in diameter. It is frequently particularly advantageous to mount at least the front wheels of the vehicle independently, and the weight and loads carried by the wheels increases the difficulty of securing the wheels to the vehicle. In addition, it is preferable to provide a brake disc system for each wheel, operable independently of one another and so arranged that one brake mechanism will automatically be brought into service in the event of failure of the other brake mechanism. During a braking operation, it has been found that the disc generates a considerable amount of heat, and the metallic materials from which the disc is constructed frequently "seizes" the elements to which it is secured, or fuses thereto; and as a consequence, it is difficult, if not impossible, to remove the disc for replacement or repair. Usually the disc is completely destroyed during removal, which is an obvious disadvantage. In order to remedy this difficulty, an annular groove is frequently provided on the opposite faces of the brake disc in order to dissipate the heat. In actual use, however, it has been found that the groove disposed outboard, or on the engaging face of the disc, is substantially completely ineffective for heat dissipation since it is completely covered by the braking surfaces of the stationary brake elements, and the outboard groove is too far removed from the heating area to accomplish any heat dissipation.